1. Field of the Invention
The present invention relates to an agent for the permanent shaping of hair containing certain new mercaptoacetamides as an active keratin-reducing substance and to a method for the permanent shaping of hair using such substances.
2. Prior Art
It is known that the classical method for achieving a permanent shaping of the hair is based on two treatment steps: In the first step, the cystine-disulfide bridges of the hair keratin are opened by means of the action of an agent containing an active reducing substance (shaping agent). The hair is then shaped into the desired form. In a second step, the cystine-disulfide bonds are closed again by means of a fixing agent, i.e. an agent containing oxidizing substances.
In classical reducing agents for permanent shaping, as shown by the pioneering work in German patent applications 948 186 and 972 424, thioglycolic acid is used, for example in the form of ammonium salt or monoethanolamine salt. Other classically used active substances are inorganic sulfites, 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, certain mercaptocarboxylic acid esters, cysteine, and derivatives of these compounds.
All these agents, however, have a number of disadvantages. Despite being effective enough, preparations based on mercaptocarboxylic acids and adjusted to be alkaline cause hair damage, which is expressed for example in increased breakage of the hair. Often these substances also place undesirable stress on the scalp.
Finally, the unpleasant odor of the reducing agents used requires an intensive addition of scent to the product. By using 2-mercaptopropionic acid (thiolactic acid) it is possible to solve some of the aforementioned problems. However, in comparison to thioglycolic acid which is generally used, the shaping achieved with thiolactic acid is limper.
Mercaptocarboxylic acid esters that make the shaping of hair possible even at low pH values are not satisfactory in terms of their tolerance by the skin and their risk of sensitization. In place of mercaptocarboxylic acid esters, mercaptocarboxylic acid amides such as thioglycolic acid amide or alkyl- or hydroxyalkyl-substituted amides have also been also used. Such compounds are known from international patent application WO-A-91/10421 and European patent application EP-A-0 455 457. These substances, like carboxylic acid esters, have a high shaping potential even at low pH values, but with regard to sensitization, they are even more critical than the esters.